Buggy code:
@ RunWith ( RandomizedRunner . class ) public class RandomizedTest extends Assert { public static final String SYSPROP_MULTIPLIER = "randomized.multiplier" ; protected static final Charset UTF8 = Charset . forName ( "UTF-8" ) ; protected static final Charset UTF16 = Charset . forName ( "UTF-16" ) ; protected static final Charset ISO8859_1 = Charset . forName ( "ISO-8859-1" ) ; protected static final Charset US_ASCII = Charset . forName ( "US-ASCII" ) ; protected static final Charset UTF32 = Charset . forName ( "UTF-32" ) ; private static final double DEFAULT_MULTIPLIER = 1.0 ; protected static RandomizedContext getContext ( ) { } protected static boolean isNightly ( ) { } protected static Random getRandom ( ) { } protected static boolean randomBoolean ( ) { } protected static byte randomByte ( ) { } protected static short randomShort ( ) { } protected static int randomInt ( ) { } protected static float randomFloat ( ) { } protected static double randomDouble ( ) { } protected static long randomLong ( ) { } protected static double randomGaussian ( ) { } protected static int randomInt ( int max ) { } protected static int randomIntBetween ( int min , int max ) { } protected static int between ( int min , int max ) { } protected static int atLeast ( int min ) { } protected static int atMost ( int max ) { } protected static boolean rarely ( ) { } protected static boolean frequently ( ) { } protected static < T > T randomFrom ( T [ ] array ) { } protected static < T > T randomFrom ( List < T > list ) { } public static double multiplier ( ) { } public static int iterations ( int min , int max ) { } public static int scaledRandomIntBetween ( int min , int max ) { } private static File globalTempDir ; private static int tempSubFileNameCount ; protected static File globalTempDir ( ) { } protected File newTempDir ( ) { } protected static File newTempDir ( LifecycleScope scope ) { } protected < T extends Closeable > T closeAfterTest ( T resource ) { } protected static < T extends Closeable > T closeAfterSuite ( T resource ) { } protected File newTempFile ( ) { } public static Object [ ] $ ( Object ... objects ) { } public static Object [ ] [ ] $$ ( Object [ ] ... objects ) { } protected static File newTempFile ( LifecycleScope scope ) { } private static String nextTempName ( ) { <START_BUG> return String . format ( "%04d" , ( ( RandomizedTest . tempSubFileNameCount ) ++ ) ) ; <END_BUG> } static void forceDeleteRecursively ( File fileOrDir ) throws IOException { } public static ServerSocket newServerSocket ( LifecycleScope scope ) throws IOException { } protected static Locale randomLocale ( ) { } protected static TimeZone randomTimeZone ( ) { } public static String randomAsciiOfLengthBetween ( int minCodeUnits , int maxCodeUnits ) { } public static String randomAsciiOfLength ( int codeUnits ) { } public static String randomUnicodeOfLengthBetween ( int minCodeUnits , int maxCodeUnits ) { } public static String randomUnicodeOfLength ( int codeUnits ) { } public static String randomUnicodeOfCodepointLengthBetween ( int minCodePoints , int maxCodePoints ) { } public static String randomUnicodeOfCodepointLength ( int codePoints ) { } public static String randomRealisticUnicodeOfLengthBetween ( int minCodeUnits , int maxCodeUnits ) { } public static String randomRealisticUnicodeOfLength ( int codeUnits ) { } public static String randomRealisticUnicodeOfCodepointLengthBetween ( int minCodePoints , int maxCodePoints ) { } public static String randomRealisticUnicodeOfCodepointLength ( int codePoints ) { } public static void sleep ( long millis ) { } public static void assumeTrue ( boolean condition ) { } public static void assumeFalse ( boolean condition ) { } public static void assumeNotNull ( Object ... objects ) { } public static void assumeTrue ( String message , boolean condition ) { } public static void assumeFalse ( String message , boolean condition ) { } public static void assumeNoException ( String msg , Throwable t ) { } public static void assumeNoException ( Throwable t ) { } public static double systemPropertyAsDouble ( String propertyName , double defaultValue ) { } public static float systemPropertyAsFloat ( String propertyName , float defaultValue ) { } public static int systemPropertyAsInt ( String propertyName , int defaultValue ) { } public static float systemPropertyAsLong ( String propertyName , int defaultValue ) { } @ SuppressWarnings ( "serial" ) private static final HashMap < String , Boolean > BOOLEANS = new HashMap < String , Boolean > ( ) { } ; public static boolean systemPropertyAsBoolean ( String propertyName , boolean defaultValue ) { } private static void checkContext ( ) { } }

Fix:
return String . format ( "%04d<seq2seq4repair_space>has-space" , ( ( RandomizedTest . tempSubFileNameCount ) ++ ) ) ;